The Angel of the North: welcome to the age of the 'enginartist'

A stunning giant sculpture three times the size of 'The Angel of the North' will for the first time see an engineer given equal billing with an artist. John Whitley meets them

Looming high above the traffic on the A1 outside Gateshead, Antony Gormley's towering Angel of the North sculpture has spawned a whole family of imitators in the North-East as councils attempt to regenerate their decaying constituencies with a nice piece of public art.

But now the scale of public sculpture is about to be changed. Before this winter's first frosts, a steel monster will creep across the debris around the old Tees Dock in Middlesbrough. At 164ft, it will stand almost three times the Angel's height and its 360ft span will stretch the length of several city streets.

This pioneer is named Temenos and will be the first of five Tees Valley giants striding across the landscape at a total cost of £15 million, the money coming from a variety of sources including Middlesbrough Football Club.

But its size is not the most radical thing about this behemoth, due for completion next year. What is even more significant is that its conceptual and technical demands have forged an entirely new idea of the artist. Instead of the sole creator, it has given birth to a two-headed visionary partnership, an "enginartist" in whom engineering and aesthetic powers meet on equal terms.

In the ego-driven stratosphere of high art and high architecture, such a willingness to share talent - and credit - is rare indeed. Though many sculptors rely on skilled assistants, they habitually claim sole ownership of the result, and starry architects are equally reluctant to share their limelight with the engineers who ensure that their masterpieces don't fall down.

As Cecil Balmond, the engineering half of this new partnership, acknowledges, "Engineering's not sexy to talk about. The annoying thing is that engineers are supposed to be calculating machines, mathematically brilliant technocrats, but they're denied creativity.

Brunel did it, and he was a hero - why can't engineering create? It is hard when you are working with someone, inventing, but your work is absorbed into the author's credit."

Balmond should know. At 65 he is the deputy chairman of Arup, long the world's leading structural engineers, and has tangled with architects from "Big Jim" Stirling to Daniel Libeskind and Toyo Ito. The 2006 pavilion at the Serpentine was his, with Rem Koolhaas, and so is the CCTV Tower now rising in Beijing.

But it's his current partnership with sculptor Anish Kapoor that marks a break with tradition: Temenos can claim to be the first landscape artwork in which artist and engineer share equal billing. It is, says Balmond, "on absolutely the same terms.

We both got the contract and though there is a sort of tension in our work, it's that tension that makes a collaboration. I challenge him and he challenges me."

Kapoor certainly makes a challenging partner for anyone. Now 54 and among the world's finest abstract sculptors, he makes vast, vividly glittering shapes that light up city centres from New York to Chicago and São Paulo; a winner of the Turner Prize and the Venice Biennale, he's not an obvious candidate for playing second fiddle.

But here he is, in his labyrinthine studios in south London, bubbling with ideas for the giants. Although funding for the next four is as yet a distant dream, he and Balmond have a folder full of exotic shapes.

Apart from a proposal for a 520ft serpentine footbridge at Hartlepool - a "kissing bridge", Kapoor calls it, that will advance and contract to allow boats through - these ideas remain secret. But a tower of Babel might seem appropriate, and there would certainly be space on some shoreline for one of the artist's trademark mirrors.

First, though, this odd couple must prove that they can carry through Temenos without coming to blows. "Well," laughs Kapoor, "certainly, we have heated arguments. I don't think I could work like this with anyone except Cecil. We have a very similar way of thinking about certain things - a similar approach to geometry, similar notions of form."

The pair first showed their compatibility with the installation of Marsyas in the Tate's Turbine Hall in 2002. This vast, sleekly red PVC envelope was devised and signed by Kapoor but effectively realised by Balmond: "I shaped the fabric - I wanted to explore form, that's basically what I do," says Balmond.

But the massive civil engineering project along the Tees demands a wholeheartedly symbiotic partnership. "I thought, I'm an ambitious chap but this is bloody ambitious," recalls Kapoor. "Then I made a proposal to Cecil for the whole project and we began playing around with various models.

"We throw around a range of ideas and they are mixed up with other realities like the money available, the force of the wind, can it be covered up, the eventual use of the object. In the end, with him filtering and me filtering we come up with something that we both feel good about.

"So it's not strictly me saying, here's an idea, let's make a bridge like this. There is a process like any human situation, in which there is an aesthetic world that we want to hold on to but that also has to relate to a physical logic. If we're going to do something, we want it to be done in such a way that the means by which it's achieved have a purity."

Any threats of rampant egotism may be diluted by the fact that both men originate in the East, Kapoor the son of an Indian rear-admiral and Balmond of an eminent Sri Lankan historian. And their shared preoccupation with geometry, turning space inside out, has inspired Temenos as it did Marsyas.

It is shaped from thousands of stainless steel "cords" stretched between two hoops, but this simple arrangement will provide an endless variety of vistas: "It's two rings, a pole and a lot of tension," says Kapoor with a laugh. "That's what it's about - how to do that with clarity."

Kapoor may have thought up the shape and title - "temenos" means "sacred space" in Greek - but Balmond adds the nuts and bolts: "I have this plinth and you stretch these wires up from it and it will seem to vanish and then return as you walk round it and as the light changes. It'll be mysterious, it's a sort of threading in space and it is surely the biggest risk I've ever taken."

One worth taking, though: "For me, the attraction was that he was thinking like I would like to think," says Balmond. "Put aside the fame, put aside the glory. When you begin, you come as two people for a debate - Anish comes as the artist, so he's complaining about a show or something. But then we start on the piece and about half an hour into the discussion will come a moment that matters, where we really are locked into something.

"I don't know what it is but we're trying to find something. I've tried to do that in my career all the time, and to find someone else doing it from his side kind of bonded us. We felt we were on a like journey."